Rejoice, because the Cosmos reboot is getting better and better. Despite Fox's annoying habit of jamming commercial breaks in every two seconds, the fourth episode, “A Sky Full of Ghosts,” was a riveting exploration of lookback time, relativity, and black holes.

The tribute to Sagan at the end—which compared him to a departed star whose light shines on—was a genuine heart-exploder, and the show continued its bold re-appropriation of religious language. The speed of light was described as a “commandment” and the cartoon segment about William and John Herschel riffed on the ubiquitous “Footprints in the Sand” poem. It may be a cheeky tactic, but it's undeniably a clever way to catch people's attention.

All that said, I do have to take “A Sky Full of Ghosts” to task for one glaring omission: where the hell was Caroline Herschel? Let me clarify up top that I don't expect the show to credit every scientist involved in the topics each episode covers. For example, last week I gushed about the bombastic genius Émilie Du Châtelet, but I understand why she was not in the episode—the creators were right to focus on Edmond Halley. But you can't profile William and John Herschel, and make no mention of Auntie Caroline. It simply is not done.

Caroline Herschel was William's younger sister, star vocalist, and "indefatigable assistant" (his words). She had a rough early life that included plenty of abuse and a bout of typhus that permanently stunted her growth at four-foot-three. Her mother blocked her education and her father told her she was way too ugly to ever marry, so she resigned herself to a future as a lonely house servant. It was pretty grim.

Eventually William, 12 years her senior, felt so bad over his sister's bleak existence that he invited her to leave Hanover to be his housekeeper in Bath. He had moved to England to become a musician, and his career as a choral director, organist, and composer had flourished. So in return for cleaning up after him, he gave Caroline singing lessons, only to discover she had the most beautiful voice in town. She became his principal soprano, and her talent led to offers to perform elsewhere around Europe. But she declined to sing for anyone other than William, which is a pretty apt metaphor for their relationship as a whole.

Caroline absolutely worshipped her brother, probably to an unhealthy level. If the siblings were represented as one of the binary star systems they discovered together, there is no doubt that William would be the center of gravity, and that Caroline would unquestioningly orbit him. The younger Herschel lived most of her life in her brother's shadow, where she clearly felt most comfortable.

The Herschels' house and laboratory is now a museum in Bath. Image: Roger Jones

This is an important trait that distinguishes her from scientists like Châtelet, who paved her own way and always had an innate affinity for science. Astronomy and mathematics did not come naturally to Caroline. She never even mastered multiplication tables. At the start of her career, she was only interested in astronomy because it appealed to her brother, not on the field's own merits. In some ways, this makes her later accomplishments that much more impressive, because she faced such an uphill battle in gaining the wisdom she'd eventually use to bust open the glass ceiling of her time.

She learned to grind and polish telescopic mirrors to perfection, and she took over William's duties when he was away, which helped her build a reputation of her own. On their long nights observing the skies together, she cataloged everything her brother discovered, including the planet Uranus. Eventually, the scientific community began to catch on that she was as much of an authority as William. In 1787, King George III recognized her efforts with a 50 pound pension—the first time a woman had received such an honor.

A year later, William married a widow named Mary Pitt. Caroline was not happy about losing her brother to another woman, though we don't know a lot of the details because she opted to destroy her journals from this period. However, she eventually warmed to William's wife, and the temporary rift between the siblings ended up benefiting Caroline in the long run. With her brother now a husband and a soon-to-be father, she had more time to make independent discoveries of her own, and holy hell, was she ever busy on that front.

She discovered several comets, most importantly the periodic orbit 3GP/Herschel-Rigollet—that's Herschel for Caroline, not William. Her keen expertise as a celestial observer catapulted her to international fame and she became by far the most famous female astronomer of her time. By the time she died at the ripe old age of 97, she had racked up many awards and medals. She was the rare woman lucky enough to experience the recognition she deserved within her own lifetime.

Cosmos missed an obvious opportunity to include this bizarre yet brilliant woman as an essential member of the Herschel family. What's doubly confusing about her absence is that in addition to her intimate partnership with her brother, she also shared a very close bond with William's polymath son John. She delighted in encouraging her nephew's curiosity, and worked with him on nebulae catalogues and other projects after William's death. The affection between the pair was mutual, and John named his firstborn after his devoted aunt.

For an episode all about ghosts and the unseen forces of the universe, it's kind of ironic that the creators forgot to slip in even the slightest mention of Caroline Herschel's life and career. She may have walked in her big brother's wake, but she left her own footprints in the sand too. And, just to milk that poem's metaphor to its fullest, there's no doubt that she carried William and John as much as they carried her.